The objective of Evolved Universal Terrestrial Radio Access (E-UTRA) and Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) is to develop a radio access network toward a high-data-rate, low-latency, packet-optimized system with improved system capacity and coverage. In the evolution of UMTS, a new project called 3GPP LTE (Long Term Evolution) within the Third Generation Partnership Project (3GPP) has been proposed to cope with future requirements of UMTS. LTE has introduced new schemes on the air interface for the uplink and downlink transmissions: Orthogonal Frequency Division Multiple Access (OFDMA) for the downlink and Frequency Division Multiple Access (FDMA) for the uplink.
LTE needs have compelled system designers to search for ways to increase channel capacity including increasing communications efficiency over the radio interface between radio networks and mobile units. A large portion of the radio bandwidth available at this interface is allocated to carrying substantive traffic between mobile stations and the radio network. However, there is also a large amount of control information that must be transmitted between mobile stations and the radio network to perform various operations such as mobile registration, call setup, handover, etc. Some of these operations occur quite frequently. Where possible, it is desirable to reduce the volume and frequency of such signaling to increase the amount of radio bandwidth available for substantive traffic, (i.e., increased system capacity).
For real time services such as Voice over Internet Protocol (VoIP), the search for ways to increase channel capacity has led to an increase in L1/L2 control channel overhead and is undesirable. It is to this end, as well as others, that there is a need for managing the resource allocation and signaling for group scheduling in wireless communications.
There are two schedulers in the E-UTRAN Node B (eNB) allocating physical resources; one for the uplink and one for downlink. The schedulers grant the right to transmit on a per User Equipment (UE) basis. The resource assignment comprises of physical resource blocks (PRBs) and a modulating and coding scheme (MCS). These resources are allocated for one or multiple Transmission Time Intervals (TTIs). A PRB is a sub band of the frequency domain during one TTI in the time domain.
The characteristics of real time services, such as VoIP with small packets and constant inter-arrival time, make the baseline scheduling alternatives less suitable. With dynamic scheduling, many small packets result in a great deal of overhead. On the other hand, persistent scheduling uses less signaling but uses the bandwidth inefficiently during silent periods, which are common during voice communication. To better utilize the resources with less signaling overhead, the strategy of group scheduling and non-persistent scheduling is suggested. Both approaches take advantage of the silent periods which are frequent in VoIP and have less signaling overhead than dynamic scheduling.
Group scheduling is a non-dynamic scheduling approach where users are divided into groups that get scheduled dynamically. Within a group, the UEs are assigned resources using a set of predefined formats. The formats define how the resources are divided between the UEs.
Non-persistent scheduling uses predefined allocations, but switches dynamically between silent periods and talk-spurts. Retransmissions are scheduled dynamically and on any available resource. In downlink, the eNB can avoid collisions by not transmitting to more than one UE at a time. This means that transitions between talk and silent periods can be done without reassigning persistent resources. Dynamic scheduling of these resources can still be allowed for another UE during silent periods without collisions.
In uplink however, the predefined resource cannot be used by another UE since it is not known when the predefined resource will be used for transmission. Different methods to perform signal switching between silent periods and talk spurts have therefore been suggested.
Group scheduling has been proposed to provide semi-dynamic scheduling for VoIP services that can solve the problems of voice activity change and Hybrid Automatic Repeat Request (HARQ) retransmission collision problems. The improvement for group scheduling has been proposed to adapt to link conditions and HARQ operations such as asynchronous HARQ for VoIP services. The resource index table proposed to be used for group scheduling is shown in FIG. 1.
If the user's application requires sporadic resources, (such as Hypertext Transport Protocol (HTTP) traffic), the system resources are best utilized if they are assigned on an “as needed” basis. In that case, the resources are explicitly assigned and signaled by the layer 1 control channel. If the type of service that the user is carrying out or the Quality of Service (QoS) profile of a user or application requires periodic or continuous allocation of resources, (such as VoIP), then periodic or continuous signaling of assigned Physical (PHY) resources may be avoided if persistent allocations are allowed. Persistent allocations are those PHY resource assignments that are valid as long as an explicit de-allocation is not made. The objective of having persistent scheduling is to reduce L1/L2 control channel overhead especially for VoIP traffic.
Providing persistent and non-persistent resource allocations are required for an efficient support of different types of data-transfer applications. The PHY resources assignments in the downlink (DL) of E-UTRA can be made valid for either a predetermined duration of time (non-persistent assignments) or an undetermined duration of time (persistent assignments). Since the assignment messages may target both the intended recipient of the assignment as well as any current owner of the resources specified by the assignment, they may be multicast. The control channel structure should allow for a UE to decode control channel messages targeting other UEs. However, there are several drawbacks that have been encountered when group scheduling is used for VoIP services on LTE system.
When different UEs are grouped for VoIP, use of a resource allocation table for signaling is necessary. But this will inevitably bring more signaling overhead if all resource related information has to be signaled through Radio Resource Control (RRC) signaling, which is a very inefficient way of allocating resources. Additionally, when only some of the UEs within one group are using VoIP services, there is no efficient resource allocation method such that only those UEs that are using VoIP resources are allocated resources.
For all group scheduling proposals, there are no operating procedures or signaling specified when real time (RT) and non-real time (NRT) services are supported simultaneously. There are also no operating procedures or signaling specified when one or more UEs finish their VoIP service early within a group. In addition, there are no operating procedures or signaling specified when one or more UEs need the new VoIP service within a cell.
To adapt to link conditions in current systems, an increasing amount of radio resources are allocated to a group of UEs in the resource allocation table. Consequently, if all radio resources in one allocation table are used, then it will be a waste of resources as they are dedicated only to that particular group of UEs.
It is possible that one or more UEs may finish their VoIP service and terminate their association within a group for a long period, (not the VoIP silent period), or that one or more UEs may need new VoIP services and need new grouping management, and existing methods do not provide for efficient allocation of resources for such a scenario.